1. Technical Field of the Invention
The present invention relates to an original illuminating apparatus for use in a copying machine, image reader and the like for copying and reading an image of an original, and more particularly to an original illuminating apparatus which can be used by changing a plurality of light sources for copying and reading color images by decomposing colors into each color required.
2. Brief Description of the Prior Art
A color decomposition method is used when a color image of an original is copied in color or when the color image is read as an image signal and provided with color data. Generally, two methods of decomposition are utilized, a first method being performed by using a white light source and a color decomposition filter in combination and a second method by jointly installing a plurality of light sources provided with different spectra distribution.
In the first method, all the light from a light source can not be utilized excepting only that part of the light which penetrates a filter. The effective availability of light is, therefore, low and several times more light amount is required at the light source than when it is used without a filter thus inviting an unfavorable tendency of increasing the consumption of electricity and calorific value.
In the second method, a plurality of light sources are provided jointly, however, the distance between the position that the light sources are disposed and an object to be illuminated becomes longer as a result of the space the light sources occupy. The light sources are thus separated more excessively away from an object to be illuminated than when there is only one light source, and the intensity of illumination is lowered by the square of the distance separated. It is necessary to increase the light amount of the light source by the intensity of illumination lowered. A sub-reflector is used to eliminate the shade of any bump made at the edge of an original when it is placed on an original table and illuminated for copying or reading the image. In this case, the same number of sub-reflectors as light sources has to be disposed at the positions corresponding to the light sources. Hence, an apparatus becomes larger in size and causes a corresponding rise in cost.
Japanese Published Unexamined patent application No. 189365/1984 discloses an illuminating apparatus which solves such problems.
As shown in FIG. 1, a plurality of light sources, a, b and c, are supported to rotatively move properly to an illuminating position. The light sources a, b and c are fixedly disposed on a rotating member d and are rotatively moved properly to the illuminating position in accordance with the rotation of the rotating member. When one of the light sources a, b or c is positioned at the illuminating position, two other light sources are evacuated from the illuminating position, and therefore, the light source being used may be moved nearer to an illuminating object on the limiting condition that the correlative rotation of a plurality of light sources a, b and c do not interfere with another component part. When every one of the light sources a, b and c are used, a sub-reflector e can be used in common since they are all at the illuminating position thereby restraining the apparatus from becoming large in size and complicated in structure to some extent.
However, in this light-source rotating system, a plurality of light sources a, b and c only be moved to the illuminating position by correlative rotation with the rotating member d and can not move more nearer to the illuminating object as compared with the case when each of the light sources a, b and c singularly can be located nearer to the illuminating object within the limit that each of them does not interfere with other operative parts. Accordingly, the light amount of the light sources has to be increased more than the case when one light source is used thereby increasing the consumption of electricity and calorific value.